Methods and Systems for Retaining Grinding Efficiency During Backgrinding of Through-Via Substrates

ABSTRACT

Methods and systems for retaining grinding efficiency during a backgrinding process such as, for example, backgrinding of a through-via substrate such as an embedded through silicon via wafer. A grinding fluid may include a chemical agent that is configured to remove accumulated materials from the grinding wheel.

BACKGROUND OF THE INVENTION

The present methods, devices, and systems relate generally to the field of semiconductor fabrication, and more particularly to the backgrinding of substrates to produce through vias.

Fabrication of vertically integrated semiconductor devices, commonly referred to as “3D interconnect,” may involve the formation of through vias by backgrinding a substrate to expose fill material (e.g., conductor material) from the substrate back side (the side of the substrate from which backgrinding process removes material). Backgrinding using a grinding wheel may result in removed portions of the fill material adhering to the abrasive material of the grinding wheel. This build up of accumulated fill material may cause degradation of the performance of the grinding wheel, resulting in decreased grinding efficiency during the backgrinding process.

SUMMARY OF THE INVENTION

Embodiments of the present methods for retaining grinding efficiency during a backgrinding process include backgrinding a substrate using a grinding wheel, and using a grinding fluid during the backgrinding of the substrate. The grinding wheel may have an abrasive material configured to remove a substrate material from the substrate during the backgrinding process. The grinding fluid may include a chemical agent that is configured to remove an accumulated portion of the substrate material from the abrasive material.

In some embodiments, the chemical agent is configured to remove the accumulated portion from the abrasive material by chelating the accumulated portion. In some embodiments, the chemical agent includes a citrate. In some embodiments, chemical agent includes a succinate. In some embodiments, the chemical agent includes a benzotriazole.

In some embodiments of the present methods, the grinding fluid further includes a second chemical agent that is configured to etch the accumulated portion. Some embodiments further include adjusting the pH of the grinding fluid to facilitate the chelating of the accumulated portion.

Some embodiments of the present methods further include cleaning the grinding wheel prior to backgrinding the substrate using a pre-grinding chemical agent. The pre-grinding chemical agent may be configured to remove a previously accumulated portion of a previous substrate material from the abrasive material. In some embodiments, the pre-grinding chemical agent may be configured to remove the previously accumulated portion from the abrasive material by chelating the previously accumulated portion.

In some embodiments, the pre-grinding chemical agent may include a citrate. In some embodiments, the pre-grinding chemical agent may include a succinate. In some embodiments, the pre-grinding chemical agent may include a benzotriazole.

In some embodiments, cleaning the grinding wheel prior to backgrinding the substrate further includes using sonic agitation. In some embodiments, cleaning the grinding wheel prior to backgrinding the substrate further includes using a contact-cleaning brush.

Embodiments of the present systems for performing a backgrinding process include a pedestal configured to support a substrate, a grinding wheel configured to backgrind the substrate, and a fluid source configured to deliver a grinding fluid to the substrate while the grinding wheel backgrinds the substrate. The grinding wheel may include an abrasive material configured to remove a substrate material from the substrate during the backgrinding process. The fluid source may be configured to deliver a grinding fluid to the substrate while the grinding wheel backgrinds the substrate. The grinding fluid may include a chemical agent that is configured to remove an accumulated portion of the substrate material from the abrasive material by chelating the accumulated portion.

In some embodiments of the present systems, the chemical agent may include a citrate. In some embodiments, the chemical agent may include a succinate. In some embodiments, the chemical agent comprises a benzotriazole.

Some embodiments further include a cleaning extension configured to deliver a cleaning fluid to the grinding wheel. The cleaning fluid may include a pre-grinding chemical agent that is configured to remove a previously accumulated portion of a previous substrate material from the abrasive material by chelating the previously accumulated portion.

In some embodiments of the present systems, the pre-grinding chemical agent may include a citrate. In some embodiments, the pre-grinding chemical agent may include a succinate. In some embodiments, the pre-grinding chemical agent may include a benzotriazole.

Any embodiment of any of the present methods and systems may consist of or consist essentially of—rather than comprise/include/contain/have—the described functions, steps and/or features. Thus, in any of the claims, the term “consisting of” or “consisting essentially of” may be substituted for any of the open-ended linking verbs recited above, in order to change the scope of a given claim from what it would otherwise be using the open-ended linking verb.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present methods and systems. The drawings illustrate by way of example and not limitation. Identical reference numerals do not necessarily indicate an identical structure. Rather, the same reference numeral may be used to indicate a similar feature or a feature with similar functionality. Not every feature of each embodiment is labeled in every figure in which that embodiment appears, in order to keep the figures clear.

FIG. 1 depicts one embodiment of the present systems for retaining grinding efficiency during a backgrinding process.

FIG. 2 is a cross-sectional view of the grinding wheel, substrate, and pedestal of an embodiment of the present systems, viewed from plane 2-2 of FIG. 1. Vias and fill material of the substrate are depicted.

FIG. 3 is a detailed view of a grinding wheel of an embodiment of the present systems and a substrate undergoing a backgrinding process. Abrasive material of the grinding wheel and removed substrate material accumulated on the abrasive material are depicted.

FIG. 4 is a detailed view of a grinding wheel of an embodiment of the present systems. The abrasive material of the grinding wheel has a previously accumulated portion of a substrate material from a previous backgrinding process.

FIG. 5 is a flow chart flow chart depicting an embodiment of the present methods for retaining grinding efficiency during a backgrinding process.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”) and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. Thus, a method comprising certain steps is a method that includes at least the recited steps, but is not limited to only possessing the recited steps. Likewise, a device or system comprising certain elements includes at least the recited elements, but is not limited to only possessing the recited elements.

The terms “substantially,” “about,” and their variations are defined as being largely but not necessarily wholly what is specified as understood by one of ordinary skill in the art, and in one non-limiting embodiment, the substantially refers to ranges within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5% of what is specified.

The terms “a” and “an” are defined as one or more than one, unless this application expressly requires otherwise. The term “another” is defined as at least a second or more.

In one aspect, the present disclosure provides embodiments that are methods for retaining grinding efficiency during a backgrinding process. Another aspect of the present disclosure provides systems for performing a backgrinding process. These systems may be configured to perform methods for retaining grinding efficiency during a backgrinding process such as, for example, backgrinding of a through-via substrate such as an embedded through silicon via wafer. A grinding fluid may include a chemical agent that is configured to remove accumulated materials from the grinding wheel.

An embodiment of the present system for performing a backgrinding process is depicted in FIG. 1. In this embodiment, system 10 is configured to perform a method for retaining grinding efficiency during a backgrinding process. System 10 may include pedestal 100 that is configured to support substrate 500. Mechanical clamping, electrostatic clamping, vacuum clamping, or any other suitable method for fixing substrate 500 to pedestal 100 may be employed by embodiments of the present systems.

System 10 may also include grinding wheel 200 that is configured to backgrind substrate 500. Grinding wheel 200 may have an abrasive material 210 (see FIGS. 3-4) that is configured to remove material from substrate 500 through abrasion accomplished by direct physical contact between grinding wheel 200 and substrate 500. Abrasive material 210 may comprise, for example, diamond, ceramics such as boron corbonitride, and/or metal. Grinding wheel 200 may be configured to accomplish the removal of material from substrate 500 via controlled movement of grinding wheel 200. This movement may be, for example, rotational (e.g., a rotating grinding head), linear (e.g., a grinding head that translates in a linear or arced path, or a combination of linear or arced paths), or a combination or rotational and linear (e.g., a rotating grinding head that also translates in a linear or arced path, or a combination of linear and arced paths).

Referring to FIG. 2, substrate 500 may include via 510 that are filled with fill material 520. Substrate 500 may be a silicon wafer, and fill material 520 may be a metal such as, for example, Al, Ti, TiN, Cu, Ta, TaN, W, or any other conductor that may be suitable for use with a silicon wafer. In other embodiments of the present systems, substrate 500 may be a substrate comprising a semiconductor material other than silicon (e.g., GaAs, Germainium) and fill material 520 may be any conductor that may be suitable for use with that semiconductor material. Substrate 500 may be any substrate that is suitable for backgrinding to produce a through-via substrate (e.g., substrates used in the fabrication of integrated circuits, solar cells, liquid crystal displays).

Continuing with FIG. 2, via 510 and fill material 520 may not extend completely through substrate 500 prior to the backgrinding process. Furthermore, each individual via 510 and corresponding fill material 520 may not extend to the same depth within substrate 500 due to fabrication process variations and limitations. For example, reactive ion etch lag effects may cause via 510 of smaller diameter to have shallower depth than via 510 of larger diameter. In other examples, incomplete fill of via 510 during deposition of fill material 520 may result in varying depths of fill material 520. Backgrinding of substrate 500 using grinding wheel 200 may be employed to remove material from substrate 500 to result in substrate 500 that has via 510 and fill material 520 extending completely through substrate 500 (e.g., fill material 520 is accessible at both faces of substrate 500).

Referring also to FIG. 3, the removal of material from substrate 500 to expose fill material 520 accomplished using abrasion of substrate 500 by grinding wheel 200 may result in removed portions of fill material 520 adhering to abrasive material 210. For example, accumulated substrate material 530 may stick or bond to abrasive material 210 under appropriate temperature and pressure conditions. This build up of accumulated substrate material 530 may cause degradation of the performance of the grinding wheel 200, resulting in decreased grinding efficiency during the backgrinding process.

Embodiments of the present systems may be configured such that fluid source 300 supplies grinding fluid 310 that contains chemical agent 311. Grinding fluid 310 is generally provided to the region of abrasion of substrate 500 by grinding wheel 200 to facilitate removal of waste material that are removed from substrate 500 during the backgrinding process. In some embodiments, grinding fluid 310 may also serve to remove heat generated during the backgrinding process. The use of chemical agent 311 in the present embodiments may facilitate the retention of grinding efficiency during the backgrinding process. Chemical agent 311 may be configured to remove accumulated substrate material 530 from abrasive material 210. In some embodiments of the present systems, chemical agent 311 may comprise chelating agents such as, for example, citrates, succinates, and/or benzotriazoles. Grinding fluid 310 may also include a mild corrosion agent to facilitate etching of accumulated substrate material 530 from abrasive material 210 at a rate sufficient to prevent accumulation of accumulated substrate material 530 on grinding wheel 200, but at a rate low enough to prevent significant damage to the exposed fill material 520 within substrate 500. In some embodiments, the pH of grinding fluid 310 may be adjusted to optimize the chemical conditions for the removal of accumulated substrate material 530 from abrasive material 210 by chemical agent 311.

In some embodiments, chemical agent 311 may be selectively introduced into grinding fluid 310 at certain stages of the backgrinding process, and/or the concentration of chemical agent 311 within grinding fluid 310 may be varied during the process. For example, chemical agent 311 may be introduced after a set period of grinding (e.g., after a certain time period of backgrinding or the backgrinding of a certain number of substrates). In other embodiments, chemical agent 311 may be introduced after process monitoring determines that buildup of accumulated substrate material 530 may have occurred (e.g., measurement of process variables indicates that the backgrinding performance of grinding wheel 200 has degraded past a threshold). In some embodiments, chemical agent 311 may be introduced only at certain stages of the backgrinding process (e.g., at the later stages or the fine grinding stages of the backgrinding process).

Referring to FIG. 4, some embodiments of the present systems may include cleaning extension 400 that is configured to supply cleaning fluid 410 that contains pre-grinding chemical agent 411. Accumulated previous substrate material 630 may be present, having adhered to abrasive material 210 during previous backgrinding processes. Prior to beginning a present backgrinding processes, cleaning extension 400 may be used to deliver cleaning fluid 410 containing pre-grinding chemical agent 411 to remove accumulated previous substrate material 630 from grinding wheel 200. Pre-grinding chemical agent 411 may be configured to remove accumulated previous substrate material 630 from abrasive material 210, and may comprise chelating agents such as, for example, citrates, succinates, and/or benzotriazoles. Cleaning fluid 410 may also include a corrosion agent to facilitate etching of accumulated previous substrate material 630 from abrasive material 210. In some embodiments, cleaning fluid 410 may include more aggressive chemical agents than those used in abrasive material 210. More aggressive chemical agents may be used to quickly remove accumulated previous substrate material 630 from grinding wheel 200 because cleaning extension 400 may be used to deliver cleaning fluid 410 prior to the backgrinding of substrate 500. Because fill material 520 is not yet been exposed by the backgrinding process, potential damage to fill material 520 within substrate 500 by pre-grinding chemical agent 411 may not be as critical of a concern.

Some embodiments of the present disclosure may use sonic agitation and/or a contact-cleaning brush to enhance the removal of accumulated previous substrate material 630 from grinding wheel 200.

FIG. 5 is a flow diagram illustrating an embodiment of the present methods for retaining grinding efficiency during a backgrinding process that may be performed by, for example, an embodiment of the present systems as described above and depicted in FIGS. 1-4. Method 900 may include backgrinding a substrate using a grinding wheel that comprises an abrasive material configured to remove a substrate material from the substrate during the backgrinding process (step 902); using a grinding fluid during the backgrinding of the substrate, the grinding fluid comprising a chemical agent that is configured to remove an accumulated portion of the substrate material from the abrasive material (step 904); adjusting the pH of the grinding fluid to facilitate the chelating of the accumulated portion (step 906); and cleaning the grinding wheel prior to backgrinding the substrate using a pre-grinding chemical agent, where the pre-grinding chemical agent is configured to remove a previously accumulated portion of a previous substrate material from the abrasive material (step 908).

It should be understood that the operational flow diagram of FIG. 5 is intended only as an example, and one of ordinary skill in the art will recognize that in alternative embodiments certain block may be performed in a different order than the order depicted, certain blocks may be performed in parallel, certain blocks of operation may be omitted completely, and additional operational blocks may be added. Thus, the present methods are not intended to be limited only to the operational flow diagrams of FIG. 5, but rather such operational flow diagram is intended solely as an example that renders the disclosure enabling for many other operational flow diagrams for implementing the present methods.

Descriptions of well known assembly techniques, components, and equipment have been omitted so as not to unnecessarily obscure the present methods, apparatuses, an systems in unnecessary detail. The descriptions of the present methods and apparatuses are exemplary and non-limiting. Certain substitutions, modifications, additions and/or rearrangements falling within the scope of the claims, but not explicitly listed in this disclosure, may become apparent to those of ordinary skill in the art based on this disclosure. For example, the fixing of substrate 500 to pedestal 100 may be accomplished by for example, various methods of mechanical clamping and/or electrostatic clamping.

The appended claims are not to be interpreted as including means-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” and/or “step for,” respectively. 

1. A method for retaining grinding efficiency during a backgrinding process, comprising: backgrinding a substrate using a grinding wheel that comprises an abrasive material configured to remove a substrate material from the substrate during the backgrinding process; using a grinding fluid during the backgrinding of the substrate, the grinding fluid comprising a chemical agent that is configured to remove an accumulated portion of the substrate material from the abrasive material.
 2. The method of claim 1, the chemical agent being configured to remove the accumulated portion from the abrasive material by chelating the accumulated portion.
 3. The method of claim 2, the chemical agent comprising a citrate.
 4. The method of claim 2, the chemical agent comprising a succinate.
 5. The method of claim 2, the chemical agent comprising a benzotriazole.
 6. The method of claim 2, the grinding fluid further comprising a second chemical agent that is configured to etch the accumulated portion.
 7. The method of claim 2, further comprising adjusting the pH of the grinding fluid to facilitate the chelating of the accumulated portion.
 8. The method of claim 1, further comprising cleaning the grinding wheel prior to backgrinding the substrate using a pre-grinding chemical agent, the pre-grinding chemical agent being configured to remove a previously accumulated portion of a previous substrate material from the abrasive material.
 9. The method of claim 8, the pre-grinding chemical agent being configured to remove the previously accumulated portion from the abrasive material by chelating the previously accumulated portion.
 10. The method of claim 9, the pre-grinding chemical agent comprising a citrate
 11. The method of claim 9, the pre-grinding chemical agent comprising a succinate
 12. The method of claim 9, the pre-grinding chemical agent comprising a benzotriazole.
 13. The method of claim 9, where cleaning the grinding wheel prior to backgrinding the substrate further comprises using sonic agitation.
 14. The method of claim 9, where cleaning the grinding wheel prior to backgrinding the substrate further comprises using a contact-cleaning brush.
 15. A system for performing a backgrinding process, the system comprising: a pedestal; a grinding wheel configured to backgrind a substrate supported by the pedestal, the grinding wheel comprising an abrasive material configured to remove a substrate material from the substrate during the backgrinding process; and a fluid source configured to deliver a grinding fluid to the substrate while the grinding wheel backgrinds the substrate, the grinding fluid comprising a chemical agent that is configured to remove an accumulated portion of the substrate material from the abrasive material by chelating the accumulated portion.
 16. The system of claim 15, the chemical agent comprising a citrate.
 17. The system of claim 15, the chemical agent comprising a succinate.
 18. The system of claim 15, the chemical agent comprising a benzotriazole.
 19. The system of claim 15, further comprising a cleaning extension configured to deliver a cleaning fluid to the grinding wheel, the cleaning fluid comprising a pre-grinding chemical agent that is configured to remove a previously accumulated portion of a previous substrate material from the abrasive material by chelating the previously accumulated portion.
 20. The system of claim 19, the pre-grinding chemical agent comprising a citrate.
 21. The system of claim 19, the pre-grinding chemical agent comprising a succinate.
 22. The system of claim 19, the pre-grinding chemical agent comprising a benzotriazole. 